Photovoltaic devices, photoelectric conversion devices or solar cells are devices which convert light, especially sunlight into direct current electrical power. For low-cost mass production thin film solar cells are being of interest since they allow using glass, glass ceramics or other rigid or flexible substrates as a base material, i.e. a substrate, instead of crystalline or polycrystalline silicon. The solar cell structure, i.e. the layer sequence responsible for or capable of the photovoltaic effect is being deposited in thin layers.
The deposition of said layers is typically done in a CVD system. The reactants, e.g. precursor materials, are being fed into process stations by a so called gas shower. The substrate, e.g. a workpiece, to be treated, e.g. coated, is being placed and heated on a hot plate, i.e. a substrate carrier, to establish a preferred environment for the deposition on the surface of the substrate. Normally, at least a fraction of these reactants are deposited, whereas the residuals are being removed via exhaust means, e.g. a vacuum pump.
With conventional systems, the substrates are being transported horizontally through the system by sets of rollers, supporting the substrates from beneath. Typical substrates are rectangular or square sheets of glass, glass ceramics or crystalline glass, plastic or even metal. The rollers are usually actuated e.g. by motors via a driveshaft.
As these rollers are arranged within a process chamber, e.g. a process station of a CVD system, they are exposed to the process gases, such as reactants and/or precursor substances, and will thus get coated over time. This coating negatively influences the process performance of the system. Firstly, the rollers will get contaminated by the coating and during further use the coating on the roller will be transferred to the lower side of the substrates and will stick to it. Thus the performance of subsequent systems further treating the substrate is influenced negatively. Secondly, the coating of O-rings arranged on the roller for transporting the substrate will slowly build up and start to flake off at a certain film thickness. These flakes contaminate the process chamber and influence the coating of the substrates negatively.
Consequently, there exists a need for improving process performance of such systems.